Lower than normal brain levels of the neurotransmitter candidate GABA (gamma-aminobutyric acid) have been associated with the symptoms exhibited by certain neurological disease states. The purpose of this proposal is to identify alternate metabolic pathways for the production of GABA, to provide brain-penetrating precursors which can be converted to GABA by those pathways, and to develop a method for estimating GABA turnover using labeled glutamine and other GABA precursors. The potential for lipophilic GABA derivatives such as pyrrolidinone, the lactam form of GABA, to serve as a precursor of GABA by hydrolysis pathway will be determined. Metabolic oxidation of the amines, pyrrolidine and putrescine, will be evaluated as a pathway for GABA production. Measurement of levels of GABA, glutamic acid, and GABA precursors in brain will be accomplished with specific and sensitive mass spectrometric assays. The subcellular location of the conversion of precursors to GABA will be determined. The functional significance of precursor-induced increases in GABA levels will be assessed using several pharmacological procedures.